1. Field of the Invention
The present invention relates to a system and method for controlling a multiple cylinder internal combustion engine having a common rail fuel system using a determination of fuel spill.
2. Background Art
Common rail fuel systems are used in various types of multiple cylinder internal combustion engines, such as diesel engines, for example. An accumulator or rail is used to distribute fuel to injectors or nozzles associated with each cylinder of the engine. An engine control module communicates with various engine components including one or more fuel pumps and fuel injectors to meter the fuel delivered to each cylinder, i.e. control the quantity and timing of the fuel delivery to ultimately control the performance and emissions of the engine. The timing and quantity of the fuel delivered to each cylinder in one or more injections during each combustion cycle depends in part upon the pressure within the common rail, the energizing time of the injector solenoid, and the electromechanical response of the injector. Conventional control theory using proportional (P), integral (I), and/or derivative (D) feedback control, often in combination with open-loop feed forward (FF) control, may be used to control the pressure within the common rail by controlling the volume of fuel supplied by one or more pumps during the combustion process. The gains for the feedback controller and the open loop set points for the feed forward control are usually determined by trial and error during calibration of the engine.
To determine the amount of fuel that needs to be pumped from the fuel supply to the common rail to replace the fuel used during the combustion process and maintain a desired rail pressure, one prior art approach uses an estimate or determination of injected fuel quantity. While this approach may be acceptable for some applications, the present inventor has recognized an opportunity to improve the pressure control for common rail systems that may result in improved performance, fuel economy, and reduced emissions, particularly during transient conditions.
The present invention provides a system and method for controlling a multiple cylinder internal combustion engine using a determination of a quantity of fuel pumped rather than the quantity of fuel injected during the combustion cycle. The quantity of fuel pumped is determined using an estimate of spilled fuel in addition to the quantity of injected fuel. The spilled fuel or return fuel is the fuel supplied by the pump that is not injected into the cylinders, but is used to actuate the injectors (control fuel) or that leaks past the internal components of the injectors (leaked fuel) and is returned to the fuel supply. In one embodiment, a spilled fuel estimate is determined based on rail pressure and engine speed. Another embodiment determines a spilled fuel estimate based on separate determinations of a leakage quantity and a spill control quantity. The leakage quantity represents the amount of fuel leaked past the internal passages inside the injectors and is based on rail pressure alone. In one embodiment, the leakage quantity represents the leaked fuel quantity for all of the injectors in units of liters/hour. The spill control quantity is based on rail pressure and injector energizing time. The spill control quantity represents the fuel used to operate the injector and allow the injected fuel into the cylinder during the combustion cycle. In one embodiment, the control quantity is specified in cubic millimeters per cylinder per cycle based on a rail pressure specified in units of bar and an injector energizing time specified in units of microseconds.
The present invention also includes computer readable storage media having stored instructions executable by a computer to control rail pressure of a common rail fluid distribution system in an internal combustion engine.
The present invention provides a number of advantages. For example, the present invention provides more accurate common rail pressure control using a determination of spilled fuel based on current engine operating parameters. A more accurate determination of spilled fuel may facilitate engine calibration and ultimately be used to adjust the control system to improve performance and reduce emissions. For example, the present invention provides a more accurate means for populating a feed forward table used in open loop control. This allows the feedback controller gains to be adjusted to provide a quicker response for the rail pressure governor because an optimized feed forward table reduces the necessary contribution of the feedback controller to maintain the desired common rail pressure throughout the one or more injection events for each cylinder during each combustion cycle. In addition, an accurate spilled fuel determination facilitates detection of fuel leaks. Furthermore, separate determinations of control fuel and leaked fuel may require less memory (and a resulting reduction in calibration effort) than a single determination of spilled fuel.
Various other advantages and features of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.